Mixer and process for use

ABSTRACT

A mixer and method of using the mixer is disclosed in which a closed chambered vessel capable of both holding pressure and vacuum is charged with a mixture of elastomer and materials taken from the group of tall oil, fatty acids and residues of tall oil production. The charge mixture is heated under pressure without excessive friction heat. After the heating cycle, the mixer atmosphere is evacuated under vacuum, and then the mix is discharged.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 09/626,539,filed Jul. 27, 2000 now U.S. Pat. No. 6,310,126, entitled Mixer andProcess for Uses which is a continuation-in-part of U.S. applicationSer. No. 08/677,697, filed Jul. 10, 1996, now abandoned, entitledImproved Pavement Material which is a continuation-in-part of U.S.application Ser. No. 08/391,386, filed Feb. 21, 1995, entitled Rubberand Plastic Bonding, which is now U.S. Pat. No. 5,604,277, issued Feb.18, 1997, which is a continuation of U.S. Ser. No. 08/227,017, filedApr. 13, 1994, now U.S. Pat. No. 5,488,080, issued Jan. 30, 1996,entitled Rubber and Plastic Bonding which is a continuation of U.S. Ser.No. 07/886,338, filed May 20, 1992, now abandoned. These areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a mixer and process directed to theutilization of crumb rubber produced from scrap tire carcass byeffectively drying and converting crumb rubber to a Dry LiquidConcentrate enhancing the use of crumb rubber with asphalt,thermoplastic and chemically catalyzed materials where limited moistureis desired.

2. Description of the Prior Art

Each year there are an estimated 250,000,000 scrap tires discardedthroughout the United States. Unwanted scrap tire piles, scatteredthroughout the country, have been estimated as high as 3 billion units.The poor biodegradability of scrap tire, their tendency to trap gasesand rise to the surface in landfills, the serious fire hazard scrap tirepiles represent, and the breeding environment that unwanted scrap tirepiles offer to disease carrying pests, such as rodents and mosquitos,has caused them to be classified as a serious environmental nuisance.

Attempts to reuse the materials composing scrap tires have had verylimited economic success. Many of these involve destructivedistillation. The approaches to reuse, burn, or distill scrap tiresappear not to have been commercially successful and had little effect onreducing either the flow or accumulation of scrap tire carcasses.

Truck tire carcasses with acceptable sidewall structure are recapped.The original tread stock of a used truck tire is removed by buffing. Theresulting tire buffings, generated from the removal of the originaltread stock, have been the primary feedstock material for the UnitedStates tire generated crumb rubber industry. This utilization, however,is limited in its scope and does not address the problem presented byscrap passenger or truck tire carcasses no longer suitable to berecapped.

Other methods of using scrap tire carcasses have included burning tirechips for BTU value and low and high vacuum pyrolysis to recover oil,carbon black, steel and fiber.

Several methods have been employed to enhance the value of scrap tirederived crumb rubber in vulcanized curing procedures. These methods are:polymeric coatings to enhanced-manufacture in rubber goods, addition ofvarious quantities of tall oil derived fatty acids to adhere rubberparticles into a useful mass, sulfur additions to act as a vulcanizingagent, and various complete devulcanization processes. The generatedcrumb rubber is also used in minimal percentages with virgin rubber as afiller and mixed with hot asphalt as a modifier.

Plastics is a multibillion dollar industry which produces syntheticmaterials and products, many of which were never dreamed of only a fewyears ago. Today, civilization requires synthetic materials (artificialresins produced by chemical reactions of organic substances). Manyproducts made of plastic produced materials are produced at less costthan was possible with natural materials.

Plastics, unlike glass or aluminum, are not easily recycled back intouseful products, such as those from which they were generated. Plastics,being specifically engineered, rather than a generic material, aresorted prior to recycling. Plastics are seldom remanufactured back intothe product or part which generated them. Often, recycled plastics aremore expensive than new polymers. Examples of plastics which arerecycled include (1) high-density polyethylene (“HDPE”) and low-densitypolyethylene (“LDPE”) into boards, binds, and trash cans and (2)polyethylene terephthalate (“PET”) into carpet fiber. The markets forrecycled plastics have been slow to develop and do not appear to be ableto keep pace with the generation of new plastic materials. Once plasticsare molded or spun, they lose some of the characteristics or propertiesof the virgin material. This creates a much bigger problem than scraptires because the United States generates over 12 billion tons of scrapplastics per year, most of which is destined for deposit in landfills.

Moisture content can be a hindrance to the utilization of crumb rubberin heat driven applications. See U.S. Pat. Nos. 5,488,080 and 5,604,277,both of which are to John D. Osborn. Three common apparatus and methodsof drying known in the prior art are illustrated below, when they wereused to dry crumb rubber combined with tall oil and other fatty acids:

Compared Methods of Drying

1. The tray of a dehydration unit typical to drying foods such fruit wasloaded with 1 pound of 30 mesh crumb rubber which had been combined withtall oil, fatty acid and residues of tall oil production at a by weightratio of 10%. A Carl Fisher moisture test was performed on the mixtureyielding a pre-dried moisture content of 0.79%. The unit was operatedunder standard low heat for a period of eight hours. After discharge,the temperature was measured at 180° F. The Dry Liquid Concentrate wasagain tested for moisture by Carl Fisher. The resulting moisture contentwas measured at 0.34%.

2. A fluidized bed dryer was heated to a temperature of 200° F. A sampleof 30 mesh crumb rubber was combined with tall oil, fatty acid at 10% byweight. A Carl Fisher moisture test was performed on the mixtureyielding a pre-dried moisture of 0.87%. The Dry Liquid Concentrate wasplaced in the dryer and held for four hours. At discharge, thetemperature of the Dry Liquid Concentrate was measured at 195° F. A CarlFisher moisture test was again performed yielding moisture content of0.21%.

3. A 300-liter horizontal mixer equipped with a vacuum pump and heatedjacket was heated to 300° F. A 100 pound sample of 30 mesh crumb rubberwas combined with tall oil, fatty acids and residues of tall oilproduction at 10% by weight rate. A Carl Fisher moisture test wasperformed prior to drying yielding a result of 0.79%. A 15 minute cyclewas performed with vacuum pulled to a total of 26.4 inches hg.Temperature at discharge was measured at 211° F. A Carl Fisher moisturetest was again performed yielding moisture content of 0.14%.

Crumb rubber or cross-linked granular rubber powder is hygroscopic bynature with a latent moisture content of typically less than one percentwhen produced by industry standard crumb rubber production technology.This moisture content interferes with crumb rubber's use in many heatdriven applications such as molding with thermoplastics and blendingwith asphalt binder whose applications use heat in excess of 212° F.Chemically catalyzed applications may also require crumb rubber to havelimited moisture contents to optimize performance. Heat aging of thecrumb rubber may also cause further vulcanization or crystallization ofthe rubber polymers limiting the effectiveness of direct heat as adrying method. Crumb rubber is a poor conductor of heat requiringexcessive energy to drive off moisture. Excessive heat may also heat agethe crumb rubber limiting usefulness.

It would be desirable to develop a cost feasible economic method ofprocessing crumb rubber into a substantially dry raw material for use inheat driven applications such as thermoplastic, asphalt bindermodification, as well as moisture-sensitive chemically-catalyzedmaterials.

It is well-known in the art to use tall oil with ground rubber waste forreuse as rubber. See “Ground Rubber Waste—A Supplementary Raw Materialfor the Rubber Industry” issued by Kahl & Co.; U.S. Pat. No. 4,481,335,issued Nov. 6, 1984 to Stark, Jr. entitled “Rubber Composition andMethod”; U.S. Pat. No. 3,873,482, issued Mar. 25, 1975 to Severson etal., entitled “Pyrolyzed Tall Oil Products as Synthetic RubberTackifiers”; U.S. Pat. No. 4,895,911, issued Jan. 23, 1990 to Mowdood etal., entitled “Tall Oil Fatty Acid Mixture in Rubber”; U.S. Pat. No.4,792,589, issued Dec. 20, 1988 to Colvin et al., entitled “RubberVulcanization Agents of Sulfur and Olefin”; and U.S. Pat. No. 4,224,841,issued Jan. 13, 1981 to Frankland, entitled “Method for Recycling Rubberand Recycled Rubber Product”. Generally for the area of ground polymerelastomer operation, see U.S. Pat. No. 4,771,110, issued Sep. 13, 1988to Bouman et al., entitled “Polymeric Materials Having ControlledPhysical Properties and Purposes for Obtaining These”; and for rubberdiscussions see U.S. Pat. No. 3,544,492, issued Dec. 1, 1970 to Tayloret al., entitled “Sulfur Containing Curing Agents”; and “OrganicChemistry” by Fieser and Fieser printed 1944 by D.C. Heath & Co. Boston,pages 346 and 347.

SUMMARY OF THE INVENTION

The present invention includes a mixer and process to both surfacemodify crumb rubber with tall oil, fatty acids and residues of tall oilproduction, as well as substantially dry, to less than 0.1%, the abovementioned crumb rubber through a controlled environment mixing system.

Utilization of crumb rubber as raw material is hampered in thatvulcanization forms an irreversible chemical bond. The addition of talloil, fatty acids and residues of tall oil production swell and softenthe rubber particle to facilitate surface bonding with thermo plastics,integration with asphalt and surface bonding in crosslink applications.

In the invention the desired mixer is a closed chamber vessel capable ofboth holding pressure and vacuum. The mixing action is desired to be oflow shear, medium intensity, yielding the mixture integration of thetall oil, fatty acids and residues of tall oil production with the crumbrubber without excessive friction heat. The mixer must have a controlledtemperature environment. Typical industry machinery having the abilityto incorporate the above mentioned requirements is a properly equippedhorizontal mixer.

The process for use of the equipment is to use heat and pressure first,and then, vacuum in the addition of tall oil, fatty acids and residuesof tall oil production to crumb rubber to produce a substantially dried,non-heat aged crumb rubber dry liquid concentrate useful as a rawmaterial for manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following drawings in whichlike parts are given like reference numerals and wherein:

FIG. 1 is a side view, partly in section, of a horizontal mixer of thepreferred embodiment of the present invention showing it in a layoutdrawing of the integrated parts of the mixer system including thesupport components to create a mix chamber environment supportingpressure and vacuum;

FIG. 2 is a top view of the horizontal mixer of the preferred embodimentof the present invention; and

FIG. 3 is an internal view of the mixer interior of the preferredembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention describes a method and apparatus to surface modifyand substantially dry post-vulcanized cross-linked elastomer(s), such ascrumb rubber. Crumb rubber is a granular solid typified by poor heatconductivity and irreversible chemical bonds. Vulcanized elastomergranules or powder of crumb rubber are hygroscopic by nature with latentmoisture content of up to 1% when produced with traditional crumb rubberproduction technology. Crumb rubber, being a post vulcanized elastomer,exhibits poor bonding and flow characteristics interfering with its usein various heat driven manufacturing systems, such as thermo plasticmolding, asphalt binder modification and moisture sensitive chemicallycatalyzed applications. Poor qualities of heat transference, heat agingand the crystallization of the rubber polymers also typify crumb rubberwhen exposed to prolonged heat to drive off moisture.

Post vulcanized cross-linked elastomer(s) which have been furtherprocessed by ambient or cryogenic or wet grinding into cured rubbergranules or powder forms a primary component of the mixture to be madein accordance with this invention. The cured rubber particles used areof natural or synthetic rubber, or combination thereof, which has beensubstantially vulcanized or cured, as in the manufacture of automobileor truck tires. Scrap tires, including but not limited to, automobileand truck tires, constitute a primary source of available, useful curedrubber particles. With respect to scrap tires as a source of curedrubber particles, the mixture is equally effective with crumb rubbergenerated either from the side wall or tread of scrap automobile ortruck tire carcasses. Common rubbers useful to the invention include,but are not limited to: natural rubber (“NR”), styrene butadiene rubber(“SBR”), isoprene, neoprene, nitrile, butyl and ethylene-propylene dienrubbers. There is no need to separate the rubbers by polymer content.

The preferred dry liquid concentrate, “DLC”, is a homogeneous or uniformblend or combination or mixture of tall oil, tall oil heads, tall oilpitches, residues of tall oil production, or other fatty acids, postvulcanized elastomer(s) which have been processed into granules orpowder (e.g., crumb rubber) and converting vulcanized crumb rubber intothe DLC by absorption by the crumb rubber of such, for example, tall oilagents or other fatty acids, and then by mixing with other components.

Tall oil, fatty acids and residues of tall oil production provide theadvantage of changing the crumb rubber to a dry liquid concentrate, whenmixed with the crumb rubber, enhancing the crumb rubber's ability tobond and flow when used in thermo plastic, asphalt binder and chemicallycatalyzed manufacturing applications. Tall oil fatty acids and residuesof tall oil production may also contain a moisture content of 1% or morewhen received from various manufactures.

The “DLC” enhances the performance capabilities by accelerating the heatblending cycle of the crumb rubber with asphalt or bitumen or othermaterials, thereby reducing the cost of blending equipment and reducingrequired energy facilitating use with, for example, aggregate or asphaltof a pavement mixture.

The mixtures whose method of manufacture disclosed in this inventionsubstantially modify the temperature performance, both high and low, aswell as increase the durability of various substances, such as asphaltpavement mixtures.

As shown in FIG. 1, the preferred mixing system to combine the tall oil,fatty acids and residues of tall oil production with the crumb rubber orother post-vulcanized cross-linked elastomer includes on stands 3 mixer100 having an outer shell 1 and a mix chamber 2 defined by an innershell. The outer shell 1 and mix chamber 2 define a hollow chamber 17 inbetween shells 1, 2. Chamber 17 has sufficient space to permit hot oil(not shown) to circulate through mix chamber 17. The inner shell of mixchamber 2 is heat conductive thereby permitting the hot oil (not shown)to heat the mix chamber 2.

The mixer 100 is provided with mixer paddles 16. Mix paddles 16 extendfrom mixer outer shell 1 into mix chamber 2. Mixer paddles 16 aremounted on mixer 100 and are sealed by shaft seals 15 sized to becapable of holding between 28 inches hg and 10 psi. Motor drives 2′ areconnected by means well known in the art to mixer paddle 16 to controlthe speed of the mixer paddle 16 so that mixer paddle 16 providesagitation to materials within mix chamber 2. As shown in FIG. 3, motorand drive 2 is connected to mixer shaft 18 which drives the mix paddles16 to the appropriate foot per second rotational speed. Mix paddles 16do not come into contact with the inner wall of mix chamber 2. Themixing action is desired to be of low shear with medium intensity toprevent excessive heat build up typically produced by friction in highintensity mix systems. Medium intensity mixing systems do not have highshear nor build up excessive heat. High intensity mixing systems mayhave high shear and do build heat from friction. Crumb rubber is a highfriction material. Uncontrolled friction can heat age crumb rubbermaking it less useful. Industry standard systems, which provide thiscombination of requirements, are medium intensity horizontal mixers.

Powder feed ports 5, preferably two of them, are mounted on the top ofouter shell 1 of mixer 100 and adapted to hold pressure in the mixingchamber 2. A pulse filtration system 4 is mounted on the outer shell 1of mixer 100 at the top, between the feed ports 5. Reverse filtrationsystem 4 is a reverse pulse filtration system that allows vacuum to bedrawn when the mixer paddles 16 are turning without clogging vacuumlines or vacuum pump 10.

The mixing chamber 2 should preferably have control heating capabilityup to 400° F. For this purpose, a hot oil heating system 7 is providedas a close loop system to circulate hot oil in chamber 17. The system 7should be sized to permit heating the mix chamber 2 to temperatureranging from 250° F. to 400° F.

Loading materials into mix chamber 2 are through powder feed ports 5,which extend from outer shell 1 through to mix chamber 2 (FIG. 3). Surgebins 8 are provided to be charged with powder or granules of the crumbrubber and are designed to lock in position on top of mixer 100 ifadjacent powder feed ports 5 to deliver powder granules of the crumbrubber to feed ports 5 and thence through the outer shell 1 to mixchamber 2.

A discharge port 6 having a discharge mixer gate to hold pressure isprovided on the lowest end of mixer 100 which extends from the mixchamber 2 through the inner shell and through the outer shell 1.Accordingly, surge bins 8 when empty function to hold mix discharge fromthe gate of port 6 after the completion of the mix cycle.

A pump 9 is provided to pump tall oil by a line to oil tank storage 12.Pump 9 provides hydraulic pressure to permit the pressurized tall oil tobe metered to batch requirements by a flow valve 13. Flow valve 13discharges into intermediate storage tank 14 which acts as a holdingtank for the tall oil in readiness for each mix batch requirement.

A control system 11 is provided to control the mixing including cycletime for the process, mix chamber 2 temperature, mix paddle 16 speed andthe vacuum and pressure requirements for each mix.

The dry liquid concentrate is made by combining the crumb rubber withtall oil. The mixing chamber is heated through the hot oil system, pumpand heater 7 which are initiated and continue to operate through the mixcycle. The temperature of the mix chamber 100 is elevated to between250° and 400° F. (higher temperature results in faster cycle) andpreferably is heated up to 400° F.

The surge bin 8 is charged with up to 70% of the cubic volume of mixchamber 2 in crumb rubber. Surge bin 8 is connected to powder feed port5. The second powder feed port 5 may or may not be used to addadditional powder or pellet materials as required by a specific mix.Other powder, pellet or granular materials may be added at this timeusing the second powder feed port 5 or later in the cycle, such as, forexample, after the tall oil is added, depending on the specificrequirements. The mixer motor and drive 2 are initiated turning the mixpaddles 16 continually including both charging and discharging the mixer100. The mix chamber 2 is charged by the surge bin 8 through the feedport 5 with up to 70% of the cubic volume of the mix chamber 2 withcrumb rubber. The tall oil is metered into the mix chamber 2 fromstorage tank 14 with an atomizing spray bar powered by liquid pump 9.Crumb rubber is loaded into the mixing chamber followed by a per weightaddition of up to 40% of tall oil, fatty acids and residues of tall oilproduction and the mixing chamber is sealed. It is anticipated thatother tackifers and plasticizers, which may be added in similar fashionto tall oil, may be found useful in the invention.

During the first stages of the mix cycle the latent moisture in thecrumb rubber is allowed to build pressure in the mix chamber 2 up to 8psi and preferably between 3 and 8 psi, due to the mixer shell 2 heat.The boiling point of water is increased above 212° F. under the addedpressure. The heated moisture is a more efficient conductor of heat thanthe mixer chamber 2 inner shell. Vacuum is drawn at the end of the mixcycle by the vacuum pump 10 acting through reverse impulse filter 4 fromthe mixing chamber 2. Vacuum is drawn to between 24 and 28 inches hg.When vacuum is pulled, the boiling point of the water is lowered. Themoisture turns to steam furthering the heat transfer throughout the dryliquid concentrate. The completed mix is discharged from the mix chamber2 into an empty surge bin 8 through discharge port 6 and the cycle maythen be repeated.

The above also illustrates the use only of a horizontal medium intensitybatch mix system. A continuous system duplicating the heat, pressure,addition of tall oil and vacuum required could also be used. This use ofpressure overcomes the poor transfer of heat typical to the crumbrubber. The use of pressure speeds up heat transfer and minimizes thetime required to raise the temperature of the crumb rubber component ofthe mixture, and can be done at lower temperatures than other methods.When the pressure stabilizes or reaches 5 psi, a vacuum cycle isinitiated. The vacuum is maintained until a minimum of for example 24inches hg is obtained.

The desired temperature of the discharged dry liquid concentrate mixtureis between 200° F. and 275° F. Typical mix cycle times range between 10and 15 minutes. The mixture is a free flowing granular solid upondischarge from the mixer.

As an experiment, a 300-liter horizontal mixer equipped with a vacuumpump and heated jacket was heated to 300° F. A 100-lb sample of 30-meshcrumb rubber was combined with tall oil, fatty acids and residues oftall oil production at a 10% by weight rate. A Carl Fisher moisture testwas performed with pressure allowed to build to 4.7 psi during the firstfive minutes of the cycle. Vacuum was pulled to a total of 26.4 incheshg during the last five minutes of the cycle. Temperature at dischargewas measured at 214 ° F. A Carl Fisher moisture test was again preformedyielding moisture content of 0.013%.

This experiment illustrates the advantages in reducing cycle time aswell as increasing the effectiveness of drying by a factor of ten overthe best product experiment set out in the BACKGROUND. The presentprocess also reduces the heat aging exposure of the crumb rubber,reducing the potential crystallization of the rubber polymers byshortening the exposure time and reducing the heat of the dischargedmaterial.

It is anticipated that use of pressure generated from moisture ladenedpowders to quickly super dry, may be found useful with a wide range ofmaterials.

Because many varying and different embodiments may be made within thescope of the inventive concept herein taught including equivalentstructures or materials hereafter thought of, and because manymodifications may be made in the embodiments herein detailed inaccordance with the descriptive requirements of the law, it is to beunderstood that the details herein are to be interpreted as illustrativeand not in a limiting sense.

What is claimed is:
 1. A mixer system for combining material ofpost-vulcanized cross-linked elastomers with any tall oil, fatty acidsand residues of tall oil production (collectively “oil”) to form a dryliquid concentrate which flows, comprising: a tank having a mixingchamber, said tank including an oil heater having a heating oil closedloop system to heat the contents of said mixing chamber; a mixer mountedin said tank and extending into said mixing chamber, said mixerincluding at least one shaft seal sealing said mixing chamber; a feedport mounted on said tank and adapted to feed the elastomers into saidmixing chamber; a vacuum pump mounted to said tank adapted to evacuatesaid mixing chamber of vapor and gas; a discharge port mounted on saidtank and adapted to discharge the material from said mixing chamber; apump to feed the oil to said mixing chamber; and a pressure controllerto select pressure maintenance of vapor and gas resulting from heat fromsaid oil heater acting on the material in said mixing chamber and vacuumfor evacuating vapor and gas from said mixing chamber.
 2. The mixersystem of claim 1, wherein said at least one shaft seal is mounted on amixer shaft.
 3. The mixer system of claim 2, wherein said mixer shaft isconnected to a motor for providing low shear, medium intensity mixing.4. The mixer system of claim 3, wherein said mixer shaft drives mixerpaddles for providing low heat from friction to the material.
 5. Themixer system of claim 1, wherein said heater has the capacity to raisethe temperature in said mixing chamber to at least 250° F.
 6. The mixersystem of claim 1, wherein said heater has the capacity to raise thetemperature in said mixing chamber to at least 400° F.
 7. The mixersystem of claim 1, wherein said heater has the capacity to raise thetemperature in said mixing chamber to between 250° F. and 400° F.
 8. Themixer system of claim 1, wherein there is further provided a bin sizedto receive the elastomers and adapted to empty the elastomers into saidmixing chamber by said feed ports.